Pulsed laser diode driver

ABSTRACT

Optical systems can emit train(s) of light pulses onto objects to derive a distance between the light source and the object. Achieving meter or centimeter resolution may require very short light pulses. It is not trivial to design a circuit that can generate narrow current pulses for driving a diode that emits the light pulses. An improved driver circuit has a pre-charge path comprising one or more inductive elements and a fire path comprising the diode. Switches in the driver circuit are controlled with predefined states during different intervals to pre-charge current in the one or more inductive elements prior to flowing current through the fire path to pulse the diode.

PRIORITY DATA

This non-provisional patent application claims priority to and/orreceive benefit from provisional application (Ser. No. 62/221,708, filedon Sep. 22, 2015) entitled “PULSED LASER DIODE DRIVER” and provisionalapplication (Ser. No. 62/351,651, filed on Jun. 17, 2016) entitled“PULSED LASER DIODE DRIVER”. Both provisional applications are herebyincorporated by reference in their entirety.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates to the field of integrated circuits, inparticular to circuits for driving laser diodes.

BACKGROUND

Optical systems come in many flavors. Optical communications pulsesdiodes to transmit information; optical systems such as LIDAR,time-of-flight cameras and range finders, can pulse diodes and measurereflected light to sense the presence, distance information, depthinformation, and/or speed information of an object. These opticalsystems can be used in security systems, medical systems, automotivesystems, aerospace systems, etc.

Diodes are used often as a light source for many optical applications.Laser diodes are used often due to their ability to generate a greatdeal of light, though it is not necessary for all applications, and thechoice of the light source may naturally depend on the application.Other diodes (e.g., light-emitting diodes) or electrically-driven lightsources can be used.

Diodes can emit light as a function the current conducting through thediode. To implement an optical application, a driver is provided todrive the diode, i.e., provide that current to the diode, so that lightcan be emitted. Diode drivers can vary depending on the requirements ofthe application, system design, and constraints imposed by the circuitproviding the diodes.

BRIEF DESCRIPTION OF THE DRAWINGS

To provide a more complete understanding of the present disclosure andfeatures and advantages thereof, reference is made to the followingdescription, taken in conjunction with the accompanying figures, whereinlike reference numerals represent like parts, in which:

FIGS. 1A-B show examples of pulsed laser diode driver and diode;

FIG. 2 shows an illustrative pulsed laser diode driver circuit anddiode, according to some embodiments of the disclosure;

FIGS. 3-7 illustrate different states of the pulsed laser diode drivercircuit during different intervals, according to some embodiments of thedisclosure;

FIG. 8 shows a flow diagram illustrating a method for pulsing a laserdiode, according to some embodiments of the disclosure;

FIG. 9 shows an illustrative pulsed laser diode driver circuit anddiode, according to some embodiments of the disclosure;

FIG. 10 shows a system diagram of an illustrative pulsed laser diodedriver circuit and diode according to some embodiments of thedisclosure;

FIGS. 11-14 illustrate various driver circuit for driving multiplediodes, according to some embodiments of the disclosure;

FIG. 15 shows a timing diagram for the circuit shown in FIG. 14,according to some embodiments of the disclosure;

FIG. 16 shows another driver circuit for driving multiple diodes,according to some embodiments of the disclosure; and

FIG. 17 illustrates exemplary method for pulsing a diode, according tosome embodiments of the disclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE

Brief Overview

Optical systems can emit train(s) of light pulses onto objects to derivea distance between the light source and the object. Achieving meter orcentimeter resolution may require very short light pulses. It is nottrivial to design a circuit that can generate narrow current pulses fordriving a diode that emits the light pulses. An improved driver circuithas a pre-charge path comprising one or more inductive elements and afire path comprising the diode. Switches in the driver circuit arecontrolled with predefined states during different intervals topre-charge current in the one or more inductive elements prior toflowing current through the fire path to pulse the diode.

Challenges to Pulsing Laser Diodes

Optical systems such as LIDAR, time-of-flight cameras, and rangefinders, typically emit one or more trains of light pulses (e.g.,modulated light source) onto one or more objects, and the arrival timeof the reflected light is recorded. Based on arrival time and the speedof light, it is possible to derive the distance between the light sourceand the object.

Typically, a diode is driven with narrow and high current pulses to emita train of light pulses onto the object (which can be meters away). Thespeed of light is very fast, therefore very short light pulses areneeded to achieve meter or centimeter resolution. Accordingly, a trainof narrow current pulses is needed to drive the diode to generate thetrain of short light pulses. In some cases, the desired pulse width canbe less than 5 nanoseconds, with greater than 40 Amps of peak current,necessitating more than 20 Amps per nanosecond of di/dt during the pulserise and fall times. With such stringent requirements, it is not trivialto design a circuit which can generate the narrow current pulses fordriving the diode.

FIGS. 1A-B show examples of pulsed laser diode driver and diode, indifferent configurations but providing substantially equivalentfunctions. During a first interval, a capacitor C charges andaccumulates pulse charge, while the transistor Q (acting as a switch) isOFF so that no current is conducting through the diode D and thetransistor Q. During a second interval, the transistor Q switches ON toallow the charge to flow from the capacitor C through laser diode D toemit a short light pulse. As explained earlier, narrow and high currentpulses are needed, in some cases di/dt (change in current over change intime, or rate of current change) needs to be equal to or greater than 10or 20 Amps per nanoseconds. During the second interval, di/dt can belimited by how quickly the transistor Q turns on, and by how quicklycurrent can flow through the circuit path from capacitor C towards thediode D.

Typically, discrete level shift and gate driver integrated circuits areneeded to drive transistor Q. Generally speaking, how quickly(gate-driven) transistor Q turns on (i.e., FET turn on time) is impededby the total gate charge and Miller capacitance of the transistor Q. Onetechnique for turning on transistor Q quickly, is to provide a gatedriver which can provide a high amount of charging current to morequickly charge the gate capacitance. Consider the transistor Q having aMiller capacitance of 5 picoFarad, turning on transistor Q within 4nanoseconds may require more than an Amp of charging current. Such agate driver circuit can increase system capacity, system costs, andsystem complexity. Another technique is to use power metal-oxidesemiconductor field-effect transistors (MOSFETs), Galium Nitridefield-effect transistor (GaNFET), or avalanche transistors, which haveshort rise times and high peak currents. However, these types oftransistors can be costly and further adds complexity (such as very highsupply voltages) to the driver circuit.

Besides the challenge of turning on transistor Q quickly, inductanceL_(A) (e.g., inductance between laser diode D anode and capacitor C ofFIG. 1A, inductance between drain of transistor Q and capacitor C ofFIG. 1B) and inductance L_(B) (e.g., inductance between laser diode Dcathode and drain of transistor Q of FIG. 1A, inductance between sourceof transistor Q and laser diode D anode of FIG. 1B) limits how fast thecurrent will flow to turn on the diode D because these inductances willcause current from capacitor C to lag. These inductances are present dueto the inevitable presence of bondwires and/or conductors connectingthese circuit components. Because the required current is so high, anysmall inductance can limit how fast the current can go through thediode. One technique to address this issue is through advanced packagingtechniques, which could potentially reduce the inductance enough to makethe circuit operate faster, but these techniques suffer higher cost andassembly complexity. Furthermore, these inductances can never be made tobe zero, even with advanced packaging techniques.

Improved Pulsed Laser Diode Driver Circuit

To address the limitations described above (e.g., caused by in-circuitbondwire inductance and FET turn-on times), an improved pulsed laserdiode driver circuit provides an elegant solution. The driver circuitmay be offered in a single chip solution. FIG. 2 shows an illustrativepulsed laser diode driver circuit and diode, according to someembodiments of the disclosure. The circuit seen in FIG. 2 includes someof the same components illustrated by FIGS. 1A-B. For instance, acapacitor C1 is provided for accumulating pulse charge, and can becharged through resistor R1 (e.g., during a relatively long intervalbetween pulses). Series resistor R1 is optional. However, the circuit inFIG. 2 differs from FIG. 1A, where the circuit in FIG. 2 has not justone, but two paths for current to travel. The circuit in FIG. 2 forpulsing a (laser) diode therein includes a first circuit path comprisingone or more inductive elements (e.g., L2, L1, and L3) and a first switchM1 (e.g., the first switch M1 being between the inductances and ground),and a second circuit path comprising the diode D1 and a second switch M2(e.g., the second switch M2 being between the diode D1 and ground). L1and L3 model bondwire inductances. L2 models the inductance between thecharging capacitor C1 and the bondwire, or can also include inductancewithin the capacitor C1. L2 might be smaller than L1, L3.

Two switches M1 and M2 are provided to select which path the currenttravels during different intervals. One circuit path, i.e., a pre-chargepath, can be used for pre-charging the inductance(s) during oneinterval, and the stored energy or current in the inductance(s) can bedumped very quickly towards the diode D1 using a separate circuit path,i.e., a fire path, to turn on the diode D1 during a subsequent interval.A switch timing controller can be provided to control the switches M1and M2. The switch timing controller can vary its control signals to theswitches M1 and M2 depending on the characteristics of the pulse to begenerated (e.g., pulse width, pulse period, etc.).

Switches can be implemented using a suitable transistor (e.g.,complementary metal-oxide semiconductor (CMOS) device as illustrated inFIG. 2). The gate voltages (e.g., VG1 and VG2 as shown) can becontrolled by control signals to turn on the transistor (conductingcurrent) or turn off the transistor (not conducting current) duringdifferent intervals. Equivalently, the gate voltages can be controlledby control signals to close the switch (conducting current) or open theswitch (not conducting current) during different intervals. When aswitch is closed, current to flows through the switch with little to noresistance; when a switch is open, current does not conduct through theswitch (the switch becomes very high impedance/resistance).

A switching scheme can be implemented to control the first switch M1 andthe second switch M2, where the scheme includes pre-defined states ofthe first switch M1 and the second switch M2 during different intervals.The states of the first switch M1 and the second switch M2 allowspre-charging energy or current in the one or more inductive elements inthe first circuit path prior to flowing the energy or current throughthe second circuit path to pulse the diode.

The first circuit path can conduct current so that the inductances L2,L1, and L3 can be pre-charged prior to turning on the diode D1 to makesure the diode turn-on is no longer or less affected by the lag causedby the inductances. After some period of pre-charging of theinductances, the first circuit path becomes an open circuit so thatcurrent no longer flows through the first circuit path, and currentflows through the second circuit path. As a result, the current flowingthrough the second circuit path quickly turns on diode D1. The resultingcircuit effectively addresses the limitations of circuits such as theone seen in FIGS. 1A-B, i.e., the limited turn-on time of a FET driver,and the in-circuit inductances connecting the driver and the laser diodeto the supply.

FIG. 2 is shown as an illustration, it is understood that variations tothe circuit are envisioned by the disclosure. Other topologies and meanscan be implemented to provide the circuit path(s) for pre-charginginductances in the circuit prior to turning on the diode.

Technical Improvements and Advantages of the Improved Driver

Gate drive pulse width and period can vary by application. In somecases, the pulse width can have a minimum of 4 nanoseconds or less andmaximum of 25 nanoseconds, with a pulse repetition period having aminimum of 100 nanoseconds and maximum of 1 microsecond (or even 100microseconds). Narrower pulses are needed to increase measurementresolution and allow for higher peak power to increase signal to noiseratio (SNR). Circuit shown in FIG. 2 and an appropriate switching schemecan easily meet these application requirements.

One technical improvement of the circuit illustrated in FIG. 2 and otherembodiments following the same or similar switching scheme is that theturn-on time for the diode is no longer dependent on the FET turn-ontime (which is limited due to the gate charge and parasitic capacitancesof the transistor). Instead, switch M1 of the circuit in FIG. 2 turns onfirst to pre-charge energy or current in the inductances L2 and L1between the laser supply voltage and the laser diode D1 anode, alongwith L3 between the laser diode D1 anode and switch M1 and L5 betweenground and switch M1. The laser diode D1 remains turned-off during thepre-charge phase through isolation by open switch M2. Next, switch M2turns on. Diode D1 remains off as switch M1 shorts the inductances toground and the diode D1 provides sufficient resistance to have(practically all of) the current flow through the switch M1 instead ofthe diode D1 and the switch M2. Then, switch M1 turns off. Resistance ofM1 increases as M1 turns off, forcing the stored energy or currentpre-charged in the inductances (e.g., L2 and L1) to flow through thepath having the laser diode D1 and switch M2 very quickly. Laser diodeD1 on resistance R_(on) is can be less than several hundred milliOhms,or even less than 100 milliOhms (depending on the type of diode). Thismeans the laser diode can turn on very quickly, and the FET turn-on timeis no longer critical, since it will not limit the speed of the laserdiode D1 turn-on. The speed of the laser diode D1 turn on time nowdepends on how quickly M1 turns off (or how quickly the resistance riseswhen M1 turns off), which can be very fast (much faster than the speedof turning a transistor on, e.g., within 100's of picoseconds). Invarious embodiments, switch M2 can be closed just after switch M1 isopened, at the same time when M1 is opened, or just before switch M1 isopened. These embodiments all have the benefit of pre-charginginductances L2, L1, and L3 prior to firing of diode D1, as long as theswitch M1 is closed for a sufficient amount of time to pre-charge theenergy in the inductances L2, L1, and L3.

Another improvement of the circuit illustrated in FIG. 2 is that theinductances are no longer a limiting factor for di/dt of the current(change in current over change in time) when pulsing the diode on. Asexplained with FIGS. 1A-B, the inductances can limit the di/dt of thecurrent that can flow through the laser diode). By using the switch M1to pre-charge the circuit inductances, the circuit inductances can beincluded in the “pre-charge path” and pre-charged during the period justbefore the laser diode turns on.

Referring back to FIG. 2, in some embodiments, multiple inductances inthe circuit can be taken into account and included in one or more“pre-charge paths”, such as the inductances L2 from the supply,inductances L1, L3, and/or L4 from any bondwires connecting the laserdiode to the driver, and/or inductance L5 between the switches andground, to greatly mitigate the di/dt limitations due to theinductances.

Even in the presence of these inductances, the circuit seen in FIG. 2can achieve a di/dt exceeding 20 Amps per nanosecond (A/ns) with amodest supply voltage V_(CC) of 10 volts. Using existing circuittopologies with the same inductances results in di/di much less than 10A/ns. For Time-of-Flight applications, the depth/distance accuracyimproves with narrower pulses, and the circuit illustrated in FIG. 2along with the appropriate switching scheme can improve the performanceof the overall system by providing fastest possible rise and fall timeswith high peak currents.

Furthermore, the switches M1 and M2 of the circuit of FIG. 2 can beimplemented with standard low voltage complementary metal-oxidesemiconductor (CMOS) device. The CMOS process can facilitate integrationof the gate drive circuitry and other logic together with the highcurrent driver.

The Switching Scheme

To explain the switching scheme in greater detail, FIGS. 3-7 illustratedifferent states of the pulsed laser diode driver circuit duringdifferent intervals, according to some embodiments of the disclosure.FIGS. 3-7 show a model of the pulsed laser diode driver circuit and thediode. In some embodiments, the supply V_(CC) can be +10 V. Theembodiments disclosed herein can work with other supply voltages. Thepulsed laser diode driver circuit drives the (laser) diode D1, and thedriver circuit includes a first switch S1 and a second switch S2 (e.g.,modeling the transistors M1 and M2 seen in FIG. 2). The inductances aremodeled by inductance L for simplicity. Corresponding to FIGS. 3-7 andvarious embodiments disclosed herein, FIG. 8 shows a flow diagramillustrating a method for pulsing a laser diode, according to someembodiments of the disclosure.

FIG. 3 illustrates the state of the switches S1 and S2 for accumulatingpulse charge during a first interval (task 802). The capacitor can becharged to a desire voltage for the pulse driver circuit. Accumulatingpulse charge can include charging a capacitor. Capacitor C1 canaccumulate pulse charge, and can be charged through (optional) resistorR1 connected to a voltage supply (e.g., V_(CC)). The pulse charge islater supplied as current or energy to pre-charge inductance L and tofire the diode D1. The accumulation of pulse charge can occur during arelatively long interval between pulses. During this interval, the firstswitch S1 and the second switch S2 are open. Neither the first switch S1nor the second switch S2 conducts current. The diode D1 is off.

FIG. 4 illustrates closing a first switch S1 to conduct current throughone or more inductive elements and the first switch S1 during a secondinterval (task 804). The first switch S1 is closed, and the secondswitch S2 remains open. The first switch S1 can conduct current. Thefirst switch S1 shorts the inductance L to ground, pulling theaccumulated charge or pulse current from C1 through inductance L towardsground. During this interval, the accumulated charge or pulse currentfrom capacitor C1 flows over the circuit path 402, through inductance Land the first switch S1 to pre-charge the inductance L (e.g., includinginductance of bondwire to the diode D1). The circuit path 402 isreferred herein as the “pre-charge path”. Energy or current is stored onthe inductance L during this interval. The second switch S2 is open, andthus no current conducts through the second switch S2. Diode D1 is off.Closing the first switch completes the first conductive path 402, i.e.,the “pre-charge path” for the current to flow through the first switchS1 and the one or more inductive elements.

FIG. 5 illustrates closing a second switch S2 in series with the diodeD1 (between the diode and ground or in some alternative embodiments, thesecond switch S2 is between the diode and node 408) during a thirdinterval (task 806). The first switch S1 is closed, and the secondswitch S2 is closed. During this interval, all of the current continuesto flow through circuit path 402, since the diode D1 is stillreverse-biased and remains off.

FIG. 6 illustrates opening the first switch S1 during a fourth intervalto flow current through the diode D1 and the second switch S2 during afourth interval (task 808). The first switch S1 is open and the secondswitch S2 remains closed. During this interval, the opening of the firstswitch S1 causes the energy or current (e.g., stored in the inductanceL) to flow through the circuit path 602 through diode D1 and switch S2.The circuit path 602 is referred herein as the “fire path”. The dumpingof the current over the circuit path 602 quickly pulses and fires thediode D1, and the diode D1 turns on. The di/dt during this interval canreach 20 A/ns with an exemplary V_(CC)=+10V supply.

In some embodiments, the second switch S2 is closed at the same timewhen the first switch S1 is opened. In some embodiments, the secondswitch S2 is closed just after the first switch S1 is opened. Stepsillustrated by FIGS. 5-6, i.e., closing of the second switch S2 andopening of the first switch S1, open the first conductive path (i.e.,the “pre-charge path”) and complete a second conductive path (i.e., “thefire path”) for the current to flow through the diode D1. Closing thesecond switch S2 completes a second circuit path (i.e., “the fire path”)having the diode, and opening the first switch S1 opens a first circuitpath (i.e., “the pre-charge path”) to allow the current (previouslyflowing through the “pre-charge path”) to flow through the secondcircuit path. The relative timing of the two tasks 806 and 808illustrated by FIGS. 5-6 can vary, and the overall scheme can still havethe benefit of being able to pre-charge the inductances in the circuit.

FIG. 7 illustrates opening the second switch S2 during a fifth interval(task 810). The first switch S1 is open, and the second switch S2 isopen. Neither switches are conducting current. Both the “pre-chargepath” and the “fire path” are open and not conducting current. Aseparate interval may not be needed, as the states of the first switchS2 and the second switch S2 reverts the circuit back the illustration inFIG. 3. During this fifth interval (or equivalently, returning to thefirst interval), the capacitor C1 once again accumulates pulse chargefor the next pulse. The switching scheme continues.

The following table summarizes an exemplary switching scheme:

Interval 1 Interval 2 Interval 3 Interval 4 Interval 5* FIG. 3 4 5 6 7Task 802 804 806 808 810 Exemplary 10 ns-1 us a few ns a few ns 4 ns-25ns depends on Duration application S1 Open Closed Closed Open Open S2Open Open Closed Closed Open D1 Off Off Off On Off *can be eliminated asit serves the same purpose as Interval 1

Illustrative Circuit Topology for Pre-Charging Inductances

More complex variations of this circuit are also possible. For instance,additional switches for differential charging of the additionalinductance(s) between the laser diode cathode and ground, are possible.Other suitable topologies having the “pre-charge path”, “fire path”, andan appropriate switching scheme to implement pre-charging of inductancesand fast firing of the diode are envisioned by the disclosure.

Referring back to FIG. 2, the inductances L4 and L5 would not typicallybe bondwires, but in some cases inductances L4 and L5 are bondwires in adifferent packaging solution, and might benefit from pre-charging.

FIG. 9 shows an illustrative pulsed laser diode driver circuit anddiode, according to some embodiments of the disclosure. When switches S1and S2 are open, capacitor C1 accumulates current. When switches S1 andS2 are closed, the inductances L2, L1, L3, L7, L4, and L5 (of thepre-charge path 902) are shorted to ground, and are pre-charged by thepulse charge from C1. Switches S1 and S2 being closed completes thepre-charge path 902, which has inductances L2, L1, L3, L7, L4, and L5(in series). The diode D1 is biased in such a way that the diode D1 doesnot turn on when the inductances pre-charges, by carefully controllingthe switches S1 and S2 switching time when they are closed. Forinstance, closing S1 and S2 can complete the pre-charge path. S1 can beclosed just before closing S2, or S1 and S2 are closed simultaneously.At this time, because diode D1 is not turned on (i.e., off or reversebiased), diode D1 acts as an open circuit. Accordingly, the fire path904, having inductance L2, inductance L2, diode D1, inductance L4, andinductance L5 (in series), cannot be completed. After a period ofpre-charging, switch S1 can open, which causes the pulse current from C1and energy stored in L2 and L1 to flow to the diode D1, thus turning thediode D1 on. Phrased differently, switch S2 can be closed to completethe fire path, and opening S1 can allow the current to flow through thefire path. Opening switch S1 opens the pre-charge path and currentconducts through the fire path 904. Opening switch S2 can return thecircuit back to the state where the capacitors C1 can accumulate pulsecurrent.

Variations and Implementations

FIG. 10 shows a system diagram of an illustrative pulsed laser diodedriver circuit and diode according to some embodiments of thedisclosure. Similar to other figures, R1 and C1 are provided toaccumulate pulse charge. R1 and C1 are usually not provided on the samesubstrate as D1, and R1 and C1 can be connected to D1 through bondwiresor conductors. The diode D1 can be driven by pulsed laser diode driver1102. The pulsed laser diode driver 1102 is an integrated circuit orchip comprising switches M1, M2, gate drivers 1106 a-b, and a switchingtiming controller 1104. Switches M1, M2, gate drivers 1106 a-b, and aswitching timing controller 1104 are provided on the same substrate. Theswitch timing controller 1104 can receive a laser pulse input (logiclevel), i.e., a logic input signal, as input. The laser pulse input cansignal that D1 should turn on (e.g., a logical HIGH can signal D1 shouldturn on). Based on the laser pulse input, the switch timing controller1104 can generate appropriate control signals, e.g., voltages, tocontrol gate drivers 1106 a-b to turn M1 and M2 on or off (e.g., to openor close M1 or M2) during intervals in response to the logical inputsignal according to the switching schemes described herein. In someembodiments, the laser diode D1 and the pulsed laser diode driver 1102can be co-packaged as a single integrated package.

In some embodiments, rather than driving one laser diode, the pulselaser diode driver may be driving multiple laser diodes. In suchmulti-channel implementation, the principle operation of havingdifferent circuit paths for pre-charging and quickly firing the laserdiode still applies. Specifically, the principle operation continues tohave at least two phases: pre-charging via one circuit path (i.e.,“pre-charge path”), and firing via another circuit path (i.e., “firepath”). Circuit configurations can be implemented for use with commoncathode or common anode connections of the laser diodes, since the laserdiodes may be connected with their cathodes or anodes shorted together.This configuration may pose a challenge since the driver may need toisolate the operation of each channel. Phrased differently, whenpre-charging and firing channel 1 (i.e., laser diode 1), circuitry maybe implemented to prevent the other channels (i.e., other laser diodes)from firing. In some multichannel applications, the lasers may be pulsedseparately at various rates (i.e., 10 KHz, 100 KHz, 1M, etc.), andisolating the channels can ensure proper operation. The supply voltagesto the different lasers may also differ. The integrated circuit of FIG.10 can be adapted to include more inputs, switches, and gate drivers,since more diodes have to be selected and/or driven. The switch timingcontroller 1104 of FIG. 10 may also be adapted to not only implement theopening/closing of switches to open/complete the pre-charge and firepaths, but to also implement a selection of one or more diodes to firewhile keeping the rest of the diodes off (i.e., isolating of thechannels).

FIGS. 11-14 and 16 illustrate various driver circuits for drivingmultiple diodes. The exemplary circuits illustrate providing at leastone pre-charge path and plurality of firing paths that can select achannel/diode to fire.

FIG. 11 shows a multi-channel circuit architecture for driving (e.g., 4,but any number of channels can be included) laser diodes having a commoncathode connection (or configuration). Prior to pre-charginginductances, capacitor C is charge to a desired voltage. C is connectedto laser supply (e.g., any suitable voltage source, voltage supply) andto ground. The pre-charge path is shared among all the laser diodes. Oneor more switches dedicated to each laser diode can be used to select andfire a corresponding laser diode. The switches are opened or closeddepending on the path to be implemented to be used at a given time. Thepre-charge path is illustrated by the path of one arrow labeled“pre-charge path”. In this example, the pre-charge path includesinductances L1, L2, and L3 (in series) and the pre-charge path can becompleted by closing switch S1. An exemplary fire path for diode D1 isillustrated by the path of another arrow labeled “fire path”. In thisexample, the fire path includes inductance L1, switch S2, inductance L4,diode D1, and inductance L3 (in series). Such circuit architecture,i.e., the pre-charge path, can compensate for inductance in the groundloop path. Closing the switch S2 (while keeping other switches in serieswith the other diodes open) and opening switch S1 (after pre-charging ofinductances has occurred) can select the diode D1 from a plurality ofdiodes and fire the diode D1.

FIG. 12 shows another multi-channel circuit architecture for drivinglaser diodes having a common cathode connection (or configuration). Eachchannel has a corresponding pre-charge path and a corresponding firepath. Switches are opened or closed depending on the path to beimplemented at a given time. Keeping one or more switches open in aparticular path can ensure no current flows through that particularpath, or can ensure that a particular channel is turned off. Anexemplary pre-charge path provided for laser diode D1 is illustrated bythe path of one arrow labeled “pre-charge path”. The exemplarypre-charge path has inductances L1, L5, L6, and L3 (in series). Anexemplary fire path for laser diode D1 is illustrated by the path ofanother arrow labeled “fire path”. The exemplary fire path hasinductance L1, inductance L5, diode D1, inductance L4, and inductance L3(in series). A set of pre-charge path and fire path isreplicated/provided for the rest of the laser diodes respectively. Toavoid cluttering up the FIGURE, some of the inductances such as L5, L6,and L4, and switch S3 shown for the channel having diode D1, while arepresent in the circuit for other channels as well, are not shown for therest of the channels. This exemplary circuit architecture, i.e., thepre-charge path, can compensate for inductances in the laser anode pathand the ground loop path. One or more switches dedicated to each laserdiode or channel can be used to select and utilize a given pre-chargepath. For instance, having switches S2 and S1 closed can complete thepre-charge path for diode D1. One or more switches dedicated to eachlaser diode can be used to select and fire a corresponding laser diode.Having switches S2 and S3 closed can complete the fire path for diodeD1. To use the pre-charge path, switches S1 and S2 are closed whileswitch S3 in series with diode D1 is open. Switch S3 is closed tocomplete the fire path (but it is possible that no current will flowthrough the fire path at this point). To change from flowing currentthrough the pre-charge path to the fire path, switch S1 is opened(switch S2 remains closed) to allow the current to flow through the firepath. Switch S2 can select the channel having diode D1, switch S7 canselect the channel having diode D7, and so on.

FIG. 13 shows another multi-channel circuit architecture for drivinglaser diodes having a common cathode connection (or configuration). FIG.13 differs from FIG. 12 in that inductance L4 and switch S3 of FIG. 12are not present in FIG. 13, and L7 of FIG. 12 is not present in FIG. 12.Each channel has a corresponding pre-charge path and a correspondingfire path. Switches are opened or closed depending on the path to beimplemented at a given time. Keeping one or more switches open in aparticular pre-charge or fire path can ensure no current flows throughthat particular path, or can ensure that a particular channel is turnedoff. An exemplary pre-charge path for diode D1 is illustrated by thepath of one arrow labeled “pre-charge path”. The exemplary pre-chargepath has inductances L1, L5, L6, L7 and L3 (in series). An exemplaryfire path for diode D1 is illustrated by the path of another arrowlabeled “fire path”. The exemplary fire path has inductance L1,inductance L5, diode D1, and inductance L3 (in series). A set ofpre-charge path and fire path is replicated/provided for the rest of thelaser diodes respectively. To avoid cluttering up the FIGURE, some ofthe inductances such as L5, L6 shown for the channel having diode D1,while are present in the circuit for other channels as well, are notshown for the rest of the channels. This exemplary circuit architecturecompensates for inductances in the laser anode path, the laser cathodepath, and the ground loop path. One or more switches dedicated to eachlaser diode or channel can be used to select and utilize a givenpre-charge path. For instance, having switches S2 and S1 closed cancomplete the pre-charge path for diode D1. One or more switchesdedicated to each laser diode can be used to select and fire acorresponding laser diode. Having switch S2 closed can complete the firepath for diode D1. To use the pre-charge path, switches S1 and S2 areclosed while D1 is reversed biased or off. Because diode D1 is notturned on (i.e., off or reverse biased), diode D1 acts as an opencircuit so that no current flows through the fire path for diode D1.Switch S2 being in a closed state can complete the fire path for diodeD1, but no current will flow through the fire path at this point due tothe diode D1 being off. To change from flowing current through thepre-charge path to the fire path, switch S1 is opened (switch S2 remainsclosed) to allow the current to flow through the fire path. Switch S2can select the channel having diode D1, switch S7 can select the channelhaving diode D7, and so on.

FIG. 14 shows another multi-channel circuit architecture for drivinglaser diodes having a common cathode connection (or configuration). Inthis example, separate reservoir capacitors allow separate supplyvoltage nodes for the laser diodes. A further path having a reservoircapacitor and a switch to select this further path are implemented foreach laser diode. Switch S2 can select the channel having LD1, switch S7can select the channel having LD2. Isolation or selection of differentdiodes occurs at the supply node, by making sure that the reservoircapacitors for the channels not selected to fire have zero voltage. Byproviding different reservoir capacitors for the different diodes,different voltages (provided by having different sizes of reservoircapacitors being charged to a desired voltage) can be used for firingthe laser diodes. Each channel has a corresponding pre-charge path, acorresponding fire path, and a corresponding capacitor charge path.Switches are opened or closed depending on the path to be implemented ata given time. Keeping one or more switches open in a particular path canensure no current flows through that particular path, or can ensure thata particular channel is turned off. An exemplary pre-charge path fordiode LD1 is illustrated by the path of one arrow labeled “pre-chargepath”. An exemplary fire path for diode LD1 is illustrated by the pathof another arrow labeled “fire path”. An exemplary capacitor charge pathfor diode LD1 is illustrated by illustrated by the path of another arrowlabeled “capacitor charge path”, having reservoir capacitor labeledVCC_1. A set of pre-charge path, fire path, and capacitor charge path,is replicated/provided for the rest of the laser diodes respectively. Toavoid cluttering up the FIGURE, inductances, while are present in thecircuit, are omitted from the FIGURE. One or more switches dedicated toeach laser diode can be used to charge the corresponding capacitor. Forinstance, switch S2 is closed to complete the capacitor charge path, andallow the capacitor VCC_1 to charge to a particular supply voltage. Touse the capacitor charge path, switch S2 is closed to connect thereservoir capacitor VCC_1 to the laser supply. After the reservoircapacitor VCC_1 is charged to the particular supply voltage, switch S2is opened. One or more switches dedicated to each laser diode or channelcan be used to select and utilize a given pre-charge path. Having switchS3 closed can complete the pre-charge path for diode LD1. One or moreswitches can be used to select and fire a corresponding laser diode. Forinstance, having switch S1 closed can complete the fire path for diodeLD1. In this example, switch S1 is shared among the channels, andclosing switch S1 can also complete the fire paths for otherdiodes/channels. By ensuring that the reservoir capacitors for the otherchannels are at zero voltage (i.e., not charging those reservoircapacitors), the diodes in other channels remain off while one channelis selected to fire. To use the pre-charge path, switch S3 is closedwhile switch S1 in series with diode LD1 is open and switch S2 is openas well. Switch S1 is closed to complete the fire path (but no currentwill flow through the fire path at this point). To change from flowingcurrent through the pre-charge path to the fire path, switch S3 isopened (switch S1 remains closed and switch S2 remains open) to allowthe current to flow through the fire path. FIG. 15 shows a timingdiagram for the circuit shown in FIG. 14.

FIG. 16 shows another driver circuit for driving multiple diodes. Ratherthan driving laser diodes having a common cathode configuration, thiscircuit drives laser diodes having a common anode configuration. Theprinciple operation for quickly firing a selected diode is the same,even when the laser diodes have a common anode configuration. Anexemplary pre-charge path is illustrated by the path of one arrowlabeled “pre-charge path”. An exemplary fire path for one of the laserdiodes is illustrated by the path of another arrow labeled “fire path”.Switches are opened or closed depending on the path to be implemented ata given time. Various schemes for driving laser diodes disclosed herein,besides the scheme illustrated by FIG. 16 (which has a shared pre-chargepath) can be adapted readily to circuits where the laser diodes have acommon anode configuration. Circuits shown herein having a commoncathode configuration can be converted to common anode equivalents, asillustrated by example shown in FIG. 16.

Generally speaking, the embodiments disclosed herein are applicable tooptical systems where a fast di/dt is needed to pulse a diode. Aspreviously mentioned, these optical systems include LIDAR,time-of-flight, range finding systems. Optical systems designed fordetermining depth, distance, and/or speed can also be found in manyother systems, including sports electronics, consumer electronics,medical equipment, aerospace/military equipment, automotive electronics,security systems, etc.

In the discussions of the embodiments herein, electrical components suchas capacitors, inductors, resistors, switches, transistors, and/or othercomponents can readily be replaced, substituted, or otherwise modifiedin order to accommodate particular circuitry needs. Moreover, it shouldbe noted that the use of complementary electronic devices, hardware,software, etc. offer an equally viable option for implementing theteachings of the present disclosure.

While the disclosure describe the implementations using NMOS transistors(n-type metal-oxide semiconductor transistor(s)) devices, it isenvisioned that complementary configurations using PMOS transistor(s)(p-type metal-oxide semiconductor transistor(s)) or equivalentbipolar-junction transistors (BJTs) can also be replace one or more ofthe NMOS transistor (or transistor devices) to provide the disclosedswitches. It is understood by oneskilled in the art that a transistordevice can be generalized as a device having three (main) terminals.Furthermore, it is understood by one skilled in the art that atransistor device, during operation, can have a characteristic behaviorof transistors corresponding to devices such as NMOS, PMOS, NPN BJT, PNPBJT devices (and any other equivalent transistor devices). Variedimplementations are equivalent to the disclosed implementations usingNMOS transistors devices because the varied implementations wouldperform substantially the same function in substantially the same way toyield substantially the same result.

It is also imperative to note that all of the specifications,dimensions, and relationships outlined herein (e.g., circuit components)have only been offered for purposes of example and teaching only. Suchinformation may be varied considerably without departing from the spiritof the present disclosure, or the scope of the appended claims (if any)and/or examples. The specifications apply only to one non-limitingexample and, accordingly, they should be construed as such. In theforegoing description, example embodiments have been described withreference to particular component arrangements. Various modificationsand changes may be made to such embodiments without departing from thescope of the appended claims (if any) and/or examples. The descriptionand drawings are, accordingly, to be regarded in an illustrative ratherthan in a restrictive sense.

Note that with the numerous examples provided herein, interaction may bedescribed in terms of two, three, four, or more electrical components.However, this has been done for purposes of clarity and example only. Itshould be appreciated that the system can be consolidated in anysuitable manner. Along similar design alternatives, any of theillustrated components of the FIGURES may be combined in variouspossible configurations, all of which are clearly within the broad scopeof this Specification. In certain cases, it may be easier to describeone or more of the functionalities of a given set of flows by onlyreferencing a limited number of electrical elements. It should beappreciated that the electrical circuits of the FIGURES and itsteachings are readily scalable and can accommodate a large number ofcomponents, as well as more complicated/sophisticated arrangements andconfigurations. Accordingly, the examples provided should not limit thescope or inhibit the broad teachings of the electrical circuits aspotentially applied to a myriad of other architectures.

Note that in this Specification, references to various features (e.g.,elements, structures, modules, components, steps, operations,characteristics, etc.) included in “one embodiment”, “exampleembodiment”, “an embodiment”, “another embodiment”, “some embodiments”,“various embodiments”, “other embodiments”, “alternative embodiment”,and the like are intended to mean that any such features are included inone or more embodiments of the present disclosure, but may or may notnecessarily be combined in the same embodiments.

It is also important to note that the functions related to pulsing a(laser diode), illustrate only some of the possible functions that maybe carried out by the circuits illustrated in the FIGURES. Some of theseoperations may be deleted or removed where appropriate, or theseoperations may be modified or changed considerably without departingfrom the scope of the present disclosure. In addition, the timing ofthese operations may be altered considerably. The operational flows havebeen offered for purposes of example and discussion. Substantialflexibility is provided by embodiments described herein in that anysuitable arrangements, chronologies, configurations, and timingmechanisms may be provided without departing from the teachings of thepresent disclosure.

Numerous other changes, substitutions, variations, alterations, andmodifications may be ascertained to one skilled in the art and it isintended that the present disclosure encompass all such changes,substitutions, variations, alterations, and modifications as fallingwithin the scope of the appended claims (if any) and/or examples. Notethat all optional features of the apparatus described herein may also beimplemented with respect to the method or process described herein andspecifics in the examples may be used anywhere in one or moreembodiments.

EXAMPLES

Example A is a method for pulsing a (laser) diode, the methodcomprising: charging a capacitor to accumulate pulse charge during afirst interval; closing a first switch to conduct current through one ormore inductive elements and the first switch during a second interval;closing a second switch in series with the diode during a thirdinterval; opening the first switch during a fourth interval to flowcurrent through the diode and the second switch during a fourthinterval; and opening the second switch during a fifth interval.

Example X is a circuit for pulsing a (laser) diode therein, the circuitcomprising: a first circuit path comprising one or more inductiveelements and a first switch; a second circuit path comprising the diodeand a second switch; a capacitor for accumulating pulse charge; whereinpredefined states of the first switch and the second switch duringdifferent intervals pre-charges energy or current in the one or moreinductive elements using the pulse charge through the first circuit pathprior to flowing the energy or current through the second circuit pathto pulse the diode.

Example Y includes Example X and a switch timing controller forcontrolling the first switch and the second switch.

Other examples include method and circuit for pulsing multiple laserdiodes, which may have a common cathode or common anode configuration.

Example 1 is a diode driver circuit, comprising: a first circuit pathcomprising one or more inductive elements and one or more firstswitches, a second circuit path comprising the diode and one or moresecond switches, a capacitor for accumulating pulse charge, whereinpredefined states of the first switch and the second switch duringdifferent intervals pre-charges current in the one or more inductiveelements using the pulse charge through the first circuit path prior toflowing the current through the second circuit path to pulse the diode.

In Example 2, the Example 1 can further include a switch timingcontroller for generating control signals to the one or more firstswitches and the one or more second switches to implement the predefinedstates of the one or more first switch and the one or more second switchduring different intervals.

In Example 3, the Example 1 or 2 can further include a third switch toselect the capacitor from a plurality of capacitors corresponding to thediode and one or more further diodes for charging the selected capacitorto a predetermined supply voltage for the diode.

In Example 4, any one of the Examples 1-3 can further include a thirdcircuit path in parallel with the second circuit path having a furtherdiode and one or more third switches, wherein predefined states of theone or more second switches and the one or more third switches selectsone of the second circuit path and the third circuit path to flow thecurrent.

In Example 5, the Example 4 can further include the diode and thefurther diode being connected at the cathode or the diode and thefurther diode being connected at the anode.

In Example 6, any one of the Examples 1-5 can further include at leastpart of the first circuit path and at least part of the second circuitpath being parallel to each other. In some aspects, the “pre-chargepath” provides a parallel circuit path to the diode. Current can flowthrough this parallel circuit path in order to pre-charge at least someof the inductances present in the fire path for firing the diode whilecurrent is not flowing through the diode.

In Example 7, any one of the Examples 1-6 can further include the one ormore inductive elements being in both the first circuit path and thesecond circuit path.

In Example 8, any one of the Examples 1-7 can further include the one ormore inductive elements including bondwire inductance.

Example 9 is an apparatus for pulsing a diode, comprising: means forpre-charging energy in one or more inductive elements in a first circuitpath (corresponding to step 1702 of FIG. 17); and means for directingthe pre-charged energy to a second circuit path having the diode topulse the diode (corresponding to step 1704 of FIG. 17).

In Example 10, the Example 9 can further include means for directing thepre-charged energy comprising means for completing the second circuitpath and subsequently opening the first circuit path.

In Example 11, the Example 8 or 9 can further include means forpre-charging the energy in one or more inductive elements comprisingmeans for conducting current through a first circuit path.

In Example 12, any one of the Examples 8-11 can further include meansfor directing the pre-charged energy comprising means for selecting thesecond circuit path from a plurality of second circuit paths having thediode and one or more further diode respectively to pulse only the diodeand not the one or more further diodes, and wherein the diode and one ormore further diodes are in a common cathode or anode configuration.

The means for such apparatuses in Examples 9-12 can include circuitryillustrated by the FIGURES, to implement the method illustrated by FIG.17.

What is claimed is:
 1. A method for pulsing a laser diode, comprising:accumulating pulse charge in a charge storing element during a firstinterval; pre-charging one or more inductive elements between the chargestoring element up to a terminal of the laser diode, the one or moreinductive elements including connection inductance at the terminal ofthe laser diode, by closing a first switch directly connected to theterminal of the laser diode to conduct current through the one or moreinductive elements and the first switch and keeping a second switch inseries with the laser diode open during a second interval; and firingthe laser diode, after pre-charging the one or more inductive elements,by closing the second switch during a third interval and opening thefirst switch to flow current through the laser diode and the secondswitch during a fourth interval.
 2. The method of claim 1, wherein theconnection inductance at the terminal of the laser diode is a bondwireinductance.
 3. The method of claim 1, wherein the terminal of the laserdiode is an anode of the laser diode.
 4. The method of claim 1, whereinclosing the second switch selects and fires the laser diode from aplurality of laser diodes having a common cathode configuration orcommon anode configuration.
 5. The method of claim 1, wherein: closingthe first switch completes a first conductive path for the current toflow through the first switch and the one or more inductive elements;and opening the first switch and closing the second switch opens thefirst conductive path to allow the current to flow through a secondcircuit path having the laser diode.
 6. The method of claim 5, wherein aspeed of the current flowing through the laser diode to fire the laserdiode is not limited by the one or more inductive elements.
 7. Themethod of claim 1, further comprising: receiving a logic input signal;and generating voltages for gate drivers to open or close the firstswitch and the second switch during the first, second, third, and fourthintervals in response to the logic input signal having a specified logiclevel.
 8. The method of claim 1, wherein the one or more inductiveelements further include inductances between the charge storing elementand bondwire or conductor connected to the terminal of the laser diode.9. A laser diode driver circuit, comprising: a capacitor foraccumulating pulse charge; a first circuit path comprising one or moreinductive elements between the capacitor up to a terminal of a laserdiode and one or more first switches, wherein one of the one or morefirst switches is directly connected to the terminal of the laser diode;and a second circuit path comprising the laser diode and one or moresecond switches; wherein the one or more first switches being closed,while the one or more second switches are open, pre-charges current inthe one or more inductive elements using the pulse charge through thefirst circuit path prior to flowing the current through the secondcircuit path to pulse the laser diode.
 10. The laser diode drivercircuit of claim 9, further comprising: a switch timing controller forgenerating control signals to the one or more first switches and the oneor more second switches to implement predefined states of the one ormore first switches and the one or more second switches during differentintervals.
 11. The laser diode driver circuit of claim 9, furthercomprising: a third switch to select the capacitor from a plurality ofcapacitors corresponding to the laser diode and one or more furtherlaser diodes for charging the selected capacitor to a predeterminedsupply voltage for the laser diode.
 12. The laser diode driver circuitof claim 9, further comprising: a third circuit path in parallel withthe second circuit path having a further laser diode and one or morethird switches; wherein predefined states of the one or more secondswitches and the one or more third switches selects one of the secondcircuit path and the third circuit path to flow the current.
 13. Thelaser diode driver circuit of claim 12, wherein the laser diode and thefurther laser diode are connected in a common cathode configuration orin a common anode configuration.
 14. The laser diode driver circuit ofclaim 9, wherein at least part of the first circuit path and at leastpart of the second circuit path are parallel to each other.
 15. Thelaser diode driver circuit of claim 9, wherein the one or more inductiveelements are in both the first circuit path and the second circuit path.16. The laser diode driver circuit of claim 9, wherein the one or moreinductive elements include inductance of a bondwire or conductorconnected to the terminal of the laser diode.
 17. The laser diode drivercircuit of claim 9, wherein the one of the one or more first switchesdirectly connected to the terminal of the laser diode opens and at leastone of the one or more second switches closes, after pre-chargingcurrent in the one or more inductive elements, to flow current throughthe second circuit path.
 18. The laser diode driver circuit of claim 9,wherein a speed of the current flowing through the second circuit pathto pulse the laser diode is not limited by the one or more inductiveelements.
 19. The laser diode driver circuit of claim 9, wherein a speedof the current flowing through the second circuit path to pulse thelaser diode is not limited by a turn-on time of one of the one or moresecond switches.
 20. The laser diode driver circuit of claim 9, whereina speed of the current flowing through the second circuit path to pulsethe laser diode depends on a speed of resistance rising as the one ofthe one or more first switches directly connected to the terminal of thelaser diode opens.
 21. An apparatus for pulsing a laser diode,comprising: one or more first switches in a first circuit path, whereinone of the one or more first switches is directly connected to aterminal of a laser diode; a second switch in series with the laserdiode in a second circuit path; and a switch timing controller forcontrolling the one or more first switches and the second switch duringdifferent intervals; wherein the switch timing controller closes the oneor more first switches and opens the second switch to pre-charge energyin one or more inductive elements in the first circuit path, the one ormore inductive elements including connection inductance at the terminalof the laser diode, and subsequently closes the second switch and opensat least one of the one or more first switches to direct the pre-chargedenergy to the second circuit path having the laser diode to pulse thelaser diode.
 22. The apparatus of claim 21, wherein the second switch isclosed at the same time when the at least one of the one or more firstswitches is opened.
 23. The apparatus of claim 21, wherein the secondswitch is closed after the at least one of the one or more firstswitches is opened.
 24. The apparatus of claim 21, further comprising:further switches, in series with corresponding further laser diodes,which remain open when the second switch closes to pulse only the laserdiode and not the further laser diodes; wherein the laser diode and oneor more further laser diodes are in a common cathode or anodeconfiguration.
 25. The apparatus of claim 21, wherein the one or moreinductive elements in the first circuit path includes all inductancesbetween a charging capacitor and the terminal of the laser diode. 26.The apparatus of claim 21, wherein a rate of change of a current flowingthrough the second circuit path to pulse the laser diode exceeds 20Amperes per nanosecond with a supply voltage of 10 Volts.
 27. Theapparatus of claim 21, wherein the one or more first switches and thesecond switch are complementary metal-oxide semiconductor transistors.